JP-11-82121A shows a fuel injection controller in which an ignition timing of a main injection is detected and a pilot injection quantity is controlled based on the detected ignition timing of the main injection.
In this controller, although a pilot injection is commanded, when the ignition timing of the main injection is retarded more than a case that the pilot injection is performed, the controller determines that no pilot injection is performed due to a manufacturing dispersion of the fuel injector and the like. Then, the controller increases a pilot injection quantity.
The pilot injection, which is performed prior to the main injection, advances the ignition timing of the main injection so that a rapid combustion in the main injection is restricted. Thereby, NOx and the combustion noise can be reduced.
If possible, the combustion waveform by the pilot injection may be directly analyzed so that the pilot injection quantity can be controlled.
Since the pilot injection quantity is very small, the variation in sensor signal indicative of the combustion waveform by the pilot injection is also small. The sensor signal indicative of the combustion waveform is hardly distinguished from noises, and the combustion waveform might be erroneously detected. Hence, as shown in JP-11-82121A, the pilot injection quantity is controlled based on the ignition timing of the main injection.
The ignition timing of the main injection varies according to a fuel property such as cetane number as well as a variation in injection characteristic due to an individual difference and aging of the fuel injector. For example, even if the pilot injection quantity is unchanged, when the cetane number is different, the combustion condition such as combustion quantity per unit time varies. As the result, in a case that the pilot injection quantity is unchanged, as the cetane number decreases, the ignition timing of the main injection is retarded. As the cetane number increases, the ignition timing of the main injection is advanced. When the pilot injection quantity is increased on detecting the retard of the ignition timing of the main injection, the ignition timing of the main injection can be advanced, however, an optimum pilot injection quantity cannot be established.
The excessive pilot injection quantity causes large combustion noise and generates the smoke. The insufficient pilot injection quantity retards the ignition timing of the main injection, so that the emission is deteriorated and the combustion noise becomes large due to the rapid combustion by the main injection.
The above matters occur with respect to an ignition delay time relative to a main ignition command. When the ignition timing is varied, the ignition delay time is also varied. If the pilot injection is increased in a case that the ignition delay time is long, the ignition delay time can be reduced, however, the optimum pilot injection quantity can not be established.
The present invention is made in view of the above matters, and it is an object of the present invention to provide a fuel injection controller which is able to learn an optimum pilot injection quantity based on a variation in ignition timing of the main injection, and provide a fuel injection system using the same.
According to the inventors' study, an ignition timing and an ignition delay time of a main injection vary due to an individual difference and deterioration with age of a fuel injector and a fuel property such as cetane number. As a pilot injection quantity increases, a variation in ignition timing or ignition delay time decreases. As the pilot injection quantity decreases, the variation in ignition timing or ignition delay time increases.
The inventors have found a boundary of the pilot injection quantity in which the variation in ignition timing or ignition delay time is within a specified range even when the pilot injection quantity is varied. Such a pilot injection quantity is the optimum value.
According to the present invention, when the engine driving condition is stable and the pilot injection quantity is varied, the pilot injection quantity is learned based on a variation in ignition timing of the fuel which is injected at the main injection.
Hence, an optimum pilot injection quantity can be learned in which the variation in ignition timing is within a specified range when the pilot injection quantity is varied to the optimum quantity.
The variation in ignition timing represents not only an advanced quantity and a retard quantity of the ignition timing of the main injection but also a decreased quantity and increased quantity of the injection delay time of the main injection due to a variation in pilot injection quantity. When the ignition timing is advanced, the ignition delay time is decreased. When the ignition timing is retarded, the ignition delay time is increased. Thus, the advanced quantity and the retarded quantity of the ignition timing substantially correspond to the increased quantity and decreased quantity of the ignition delay time.